This invention relates to oil well drilling equipment, and more particularly to a so-called "bit breaker" for use in connecting and disconnecting rotary drill bits to a drill string having a drill collar, drill pipe or a so-called "sub" at its lower end.
This invention involves an improvement over conventional bit breakers comprising a generally square metal plate adapted to be fitted in the socket of a Kelly drive of a drill rig. The plate has an opening therein for receiving the lower end of a conventional tri-cone drill bit to be connected to a drill string. Conventional tri-cone bits, such as shown for example in U.S. Pat. No. 4,174,759, comprise a generally cylindrical bit body, three spaced apart legs extending down from the bit body and terminating in bearing journals at the lower end of the bit, three roller cutters rotatably mounted on the bearing journals, and three nozzles in the bit body, each directing drill fluid under pressure down in the recess between a respective pair of adjacent roller cutters.
The opening in the bit breaker is configured to correspond to the shape of the lower end of a tri-cone bit of a predetermined size. The conventional bit breaker thus has so-called "breakout lugs" extending into the opening, which are adapted to be received in the recesses in the lower end of the drill bit when positioned in the opening in the bit breaker. These breakout lugs are engageable with the drill bit and prevent its rotation relative to the bit breaker, so that upon rotation of the Kelly drive, the bit breaker and drill bit rotate along with it. This enables the Kelly drive to rotate the drill bit in one direction to effect a threaded connection between the threaded pin on the bit and a drill string having an internally threaded lower end portion, and in the other direction to disconnect the bit from the drill string.
As indicated, bit breakers of the above-noted type are designed for drill bits of a predetermined size or diameter. While it may be possible to use the bit breaker for drill bits of slightly different diameter than the predetermined diameter (e.g., 3/8 inch larger diameter) the bit breaker cannot be used for drill bits of significantly larger diameter than the design size because the bits cannot be received in the opening in the bit breaker or bits of significantly smaller diameter because the bits are not engaged by the breakout lugs for holding the bit in fixed position in the opening. Since oil and gas well drilling often involves the use of drill bits of different sizes, ranging from relatively large diameter surface bits to small completion bits, a series of bit breakers having openings of different sizes are also required. This increases the cost of bit breakers for a drill rig and poses handling and storage problems.
Moreover, bit breakers of the above-described type are not usable with drill bits of the so-called "extended nozzle" type having nozzle members extending down into the recesses between adjacent roller cutters. These extended nozzles prevent entry of the breakout lugs into the recesses of a drill bit and thus positioning of the bit in the opening in the bit breaker. Specially designed bit breakers thus are required for extended nozzle drill bits. This further increases the number (and thus the cost) of bit breakers needed for certain drilling operations.